Apparatus for concentration of solutions by selective freezing of solvent



Oct. 18, 1960 F. STEINBACHER EIAL 2,956,

APPARATUS FOR CONCENTRATION OF SOLUTIONS BY SELECTIVE FREEZING OFSOLVENT I Filed Oct. 23, 1956 2 Sheets-Sheet 1 III/In III/L Friedrichskinbacl'xcr cmoL Caaas JC/meidcr Jchmer /R INVENTORS 77/5? ATTORNEYSOct. 18, 1960 F. STEINBACHER ETAL APPARATUS FOR CONCENTRATION OFSOLUTIONS Filed Oct. 23, 1956 BY SELECTIVE FREEZING OF SOLVENT 2Sheets-Sheet 2 r edrich fieifllxcher Md W der 1mtrbck INVENTORS BY mom uMMXIYm dok THE/R ATTORNEYS Patented Oct. 18, 1960 APPARATUS FORCONCENTRATION OF SOLU- TIONS BY SELECTIVE FREEZING OF SOLVENT Friedrich'Steinbacher, Munich, Germany, and Carlos Schneider Schmerbeck, GandiaCamino de Daimuz 1, Gandia, near Valencia, Spain; said Steinbacherassignor to said Schmerheck Filed Oct. 23, 1956, Ser. No. 617,767

Claims priority, application Germany Oct. 27, '1955 7 Claims. (Cl. 6258)The present invention relates to a novel process and apparatus forconcentrating solutions. More particularly, it relates to an apparatusand continuous process for the concentration of solutions by selectivelyfreezing a portion of the solvent, and separating the solvent crystalsfrom the solute particles which are dissolved in the residual solvent.

In previous procedures for eifecting concentration by freezing of thesolvent, it has been found that the solvent solidifies in a laminar formand the crystals are of small size. As a result of the large ratiobetween the surface and volume of the solvent crystals the loss ofsolute clinging to the surface of the crystal is considerable andinefficient concentration results. In addition, the small particle sizecomplicates the separation of the solid and liquid phases.

It is accordingly an object of the present invention to provide aprocess and apparatus for selectively freezing the solvent of a solutionin such manner that the solvent crystals are of large size andnon-laminar form.

It is a further object of the invention to provide an apparatus in whichsolvent crystals can be selectively frozen out of a solution in a formwhich permits ready separation from the residual concentrated solution.

These and other objects and advantages are realized in accordance withthe present invention wherein the solution is caused to move spirally ina path extending approximately perpendicularly to the axis of a stirringdevice. As the solvent is selectively frozen, the crystals thereof tendto rise while the more concentrated residual solution drops throughgravity. The spiral motion of the solution also causes the solventcrystals to move along a similar path and, instead of the conventionallaminar form, the crystals are more compact and have a smaller ratio ofsurface to volume. The crystals are continuously Iii-directed toward thecooling surface so thaat additional frozen solvent molecules resultingfrom continued cooling of the solution add on to the already formedcrystals rather than forming new nuclei. Consequently, the solventcrystals become large in size and separation is thereby facilitated.

By making the cooling zone an annular chamber the mixing of solventcrystals of difierent sizes is avoided; rather the size of the crystalsincreases progressively from bottom to top of the chamber. Consequently,the impermeability to the solution which would result from mixing ofdiiferent size crystals is avoided and the concentrated solution canreadily be drawn oif continuously. Similarly, the solvent crystals canbe discharged continuously without appreciable quantities of solute orsolution entrained therewith.

By adding the fresh solution near the top, withdrawing concentratedsolution from the bottom, and discharging solvent crystals at the top,there will be a continuous countercurrent percolation effect which willserve to increase the amount of solvent which is frozen and will alsoensure that larger crystals are formed.

A suitable apparatus for performing the indicated process comprises avessel with walls defining an annular freezing space, either one or bothwalls being cooled. A stirring device is arranged within the freezingspace and carries stripping members which prevent the solidified solventfrom adhering to the cooled Wall. In addition, guiding members areprovided which impart to the solution a spiral motion within thefreezing space and which redirect solvent crystals toward the cooledsurface for continued growth. These guiding members may be carriedeither by the vessel or by the stirrer and the desired efiect may beachieved either through rotation of the vessel or the stirrer while theother member is stationary. The solvent crystals upon leaving thefreezing space may be directed into a percolation column wherein theyare washed by fresh solution, which solution is then passed into thefreezing chamber.

A suitable apparatus will now be described with reference to theaccompanping drawings, wherein:

Fig. l is a vertical sectional view, partly broken away, of an apparatusembodying the invention;

Fig. 2 is a top plan view of a portion of the structure shown in Fig. 1,with the cover removed;

Fig. 3 is a portion of an elevation showing the stirrer arms and guidingmembers carried thereby;

Fig. 4 is a diagrammatic development showing the sequential arrangementof the guiding members on the stirrer arms; and

Fig. 5 is a perspective view showing a portion of one of the guidingmembers.

Referring now more particularly to the drawing, in Fig. 1, there isshown a cooling apparatus 1 comprising a cylindrical vessel 2 having anouter wall 3 with a circular bottom 4, and an inner wall 5 with acircular bottom 6. The top of the annular space defined between theouter wall 3 and the inner wall 5 is covered by an annular cover 7 whichmay be formed of two portions. Both cylindrical walls 3 and 5 areprovided with cooling jackets 8 for containing a cooling agentintroduced through conduits 9 and drawn off through conduits 10. Thecooling agent may be brine which is caused to traverse a helical path 11as shown at the left in Fig. 1, or it may be a volatile refrigerantwhich cools by direct evaporation in the channels 12 welded to thecooling jackets as shown at the right in Fig. 1.

At the bottom of the annular freezing space there is provided acollector drain 13 terminating in a spout 14 for removal of theconcentrated solution and for emptying of the space when necessary.Within the an nular space there is arranged a stirrer consisting of asupporting member 16 which may be provided with a displacement body 17for reducing the capacity of the vessel, and with six arms 19 extendingvertically from supporting member 16 at equal angular intervalsthereabout. The arms 19 carry stripping members 18 staggered in verticaldirection with a slight overlap so that they sweep the walls 3 and 5along their entire height. Between adjacent arms 19 there are supportedguiding members 20 (Figs. 2 and 3) which are formed of twisted sheetmetal so as to impart to the solution in the freezing space a spiralmovement. Guiding members 21 are; also carried between adjacent arms 19and are provided with deflected blade portions (Fig. 5) which re-directthe solvent crystals toward the cooled walls of the vessel.

In Fig. 4 an illustration is given of the sequential arrangement of theguiding members 20 and 21. The efiectiveness of these members is due tothe difference in speed between the stirrer and the solution as a resultof the inertia of the latter.

In freezing devices with an inner cooling surface, in-- wardly directedguiding surfaces 22 may be arranged on the stirrer in addition tostripping members 18, the guid ing surfaces 22 approaching closely butbeing out of contact with the inner wall 5. As shown in Fig. 1, abovethe cooling jackets 8 the vessel 2 is provided with a solvent crystaldischarge arrangement consisting of a ring 23 car- ,riediby the upperends of arms 19 (Fig. 4).-and having radially directedcross pieces 24defining cells which conltain the solvent crystals, such as ice. Fromthe ring 23 the crystals pam on to a screwed portion 25 carried by thecover ,7 and move -along to be discharged from the vessel. F Thesupporting member 16 carrying the stirrer arms 19 is connected to ahollow shaft 26 disposed about the preferably stationary axle 27 of thevessel 2. Rotation of the stirrer 19 is effected by rotatable drivemember 28 which is connected with the shaft 26. Fresh solution may beintroduced into the annularfreezing space through conduit 29 or conduit30 from a percolating column connected in series with the coolingvessel.

, In place of helical and deflected strips 20 and 21, the guidingmembers may be formed as small stationary or movable propellers, assuitably shaped guiding blades or as impact baflies changing thedirection of movement of the solution. In an alternative arrangement,the stirrer may be driven from above. The stirrer arms may be providedin pairs so as to form U-shaped stirrups and the guiding members may beattached to the bottom of the annular freezing space and may projectupwardly between the U-shaped stirrer arms. In place of rotating thestirrer, the cooling vessel may be rotated while the stirreris.stationary and the same results will be achieved.

If desired, cooling agent may be provided only to one of the coolingjackets so that only one of the walls of the annular freezing space iscooled, preferably the inner one. In a further embodiment, a freezingdevice provided with inner and outer cooling jackets can be providedwith a pair of spaced stirrers rotating in opposite directions, and astationary support for the additional guiding members may be positionedbetween the stirrers. In this arrangement, the screw portion 25 may becarried by the stationary support rather than by the cover 7. The upwardpassage of the solvent crystals may be assisted by additional guidingblades in the shape of whole or subdivided helical members provided withconcentrically arranged slots for treating clear pulp-free solutions.

In place of having the cooling vessel axle 27 extending vertically,however, the vessel may be turned on its side so that the axle extendshorizontally, in which case the advance of the solvent crystals will beachieved solely by the guiding blades without taking advantage of thebuoyancy of these crystals. 7

In Fig. -1 there is also shown a percolating column which can beserially connected with the cooling vessel 2. The column comprises acylindrical tubular member 31 with a shaft 32 rotated by drive member33. The tube 31 is closed off at its top by a cover 34 through which theshaft 32 passes and the bottom 35 is connected by the conduit 30 withthe annular freezing space of the vessel 2. If the solution to beconcentrated is to be admitted to the vessel solely through thepercolating column, the conduit 29 may be wholly closed off or bothconduits 29 and 30 may be used for introduction of solution.

4 From the solvent crystal discharge outlet of vessel 2, the solventcrystals pass through conduit 36 into member 31. A screw conveyor 37carried on shaft 32 is arranged opposite conduit 36 and serves to movethe crystals upwardly, supplementing the natural buoyancy effect. Thecrystals then pass into a mixing zone 38 in which mixing flaps 39 and 40are alternately arranged on the shaft 32 screw so as not to interferewith rotation of the screw. The vertically extending cells defined byseparators 46 will be filled with the solvent crystals, e.g., ice, andthe crystals then proceed into an emptying device 49 attached to thehollow portion 43 of shaft 42 from which they are discharged throughexit pipe 50. The percolating effect can be achieved Within the freezingvessel itself by combination of the structures shown in Fig. 1 into aunitary apparatus. To this end the vessel 1 would be elongated in thedirection of advance of the ice, preferably with gradual reduction ofthe diameter. The conveying screw may be arranged either rotatably inthe stationary jacket for the frozen solvent or it can be maintainedstationary within the rotating jacket similar to element 23. 1 7

Various changes and modifications may be made without departing from thespirit and scope of the present invention and it is intended that suchobvious changes and modifications be considered Within the purview ofthe annexed claims.

We claim:

1. An apparatus for concentrating solutions by cooling to solidifyselectively a portion of the solvent and leave a more concentratedsolution, comprising a vessel having a pair of walls defining an annularfreezing space, means for cooling at least one wall of said vessel, astirring member within said freezing space, means for producing relativemovement between said vessel and said stirrer thereby to elfect movementof solution within said freezing space, stripper means carried by saidstirrer and contacting the cooled wall of said vessel so as to preventsolvent crystals from adhering to said wall, bladed guiding meansincluding a plurality of blades disposed in and extending transverselyof said annular freezing space so as to re-direct solvent crystalstoward said cooled wall, thereby causing said crystals to grow asopposed to forming many new small crystals, and helical guiding meanswithin said annular freezing space, said helical guiding means supportedby said stirrer and imparting a helical motion to the moving solution.

2. An apparatus as defined in claim 1, wherein said cooling means actson the inner wall of said vessel.

3. An apparatus as defined in claim 1, wherein said cooling means actson both walls of said vessel.

4. An apparatus as defined in claim 1, wherein said vessel is stationaryand said means for producing relative movement acts on said stirrer.

5. An apparatus as defined in claim 1, including outlet means providedin said vessel adjacent the bottom thereof for withdrawing concentratedsolution from the bottom of said annular freezing space, a percolatingcolumn, a large conduit connecting said column with the top of saidfreezing space, a small conduit connecting said column with saidfreezing space below the points of connection of said large conduit, asolvent crystal outlet adjacent the top of said column, and means forintroducing fresh solution into said column intermediate its connectionwith said large conduit and said solvent crysand the member 31. Freshsolution is introduced either tal outlet.

6. An apparatus for concentrating solutions by cooling to solidifyselectively a portion of the solvent and leave a more concentratedsolution, comprising a vessel having a wall defining a freezing space,means for cooling said wall of said vessel, a stirring member having alongitudinal axis and being disposed within said freezing space, meansfor producing relative movement between said vessel and said stirringmember thereby to effect movement of solution in said freezing space,stripper means carried by said stirring member and contacting the cooledwall of said vessel so 'as to prevent solvent crystals from adhering tosaid wall, bladed guiding means disposed within said annular freezingspace and extending in-superposed annular zones concentric with saidaxis so as to re-direct solvent crystals toward said cooled wall,thereby causing said crystals to grow as opposed to forming many newsmall crystals, and helical guiding means supported by said stirrer anddisposed within said superposed annular freezing space and extending inannular zones concentric with said axis whereby upon producing relativemovement between said vessel and said stirring member said helicalguiding means imparts to the solution a. helical motion Within saidfreezing space.

7. Apparatus as defined in claim 6 including outlet means provided insaid vessel adjacent the bottom thereof for continuously withdrawingconcentrated solution from said annular freezing space, a solventcrystal outlet adjacent the top of said annular freezing space, andinlet means adjacent the top of said annular freezing space forintroducing fresh solution into said annular freezing space.

References Cited in the file of this patent UNITED STATES PATENTS761,387 Monti May 31, 1904 2,119,182 Schuftan May 31, 1938 2,227,887Koropchak Jan. 7, 1941 2,240,463 Schlumbohm Apr. 29, 1941 2,503,395Leboeuf Apr. 11, 1950 2,552,524 Cunningham May 15, 1951 2,579,421 EganDec. 18, 1951 2,657,549 Wenzelberger Nov. 3, 1953 2,657,555 WenzelbergerNov. 3, 1953

